Network devices typically communicate via communications cables and receive power from separate power cables. For example, a personal computer (PC) may exchange Ethernet frames with an Ethernet switch via an Ethernet cable and receive power from a power source via a separate power cable. In order to eliminate the need for a separate power cable, efforts have been made to utilize network connections, such as an Ethernet cable, for providing power to the end network device.
The Institute of Electrical and Electronics Engineers (IEEE) has defined a method for powering end network devices through an Ethernet cable. Particularly, in the IEEE 802.3af standard (also known as the Power over Ethernet (PoE) standard), the IEEE has defined methods by which power source equipment (PSE) power Ethernet-connected powered devices (PDs) over an Ethernet cable. The IEEE 802.3af standard defines how a PD is detected and methods of delivering power to the PD over an Ethernet cable.
The IEEE 802.3af standard specifies power levels that the PSE must supply to different classes (i.e., classes 0, 1, 2, 3, and 4) of PDs. For example, the IEEE 802.3af standard specifies that the PSE must reserve at least 15.4 watts (W) for a class 3 PD. However, the 802.3af standard specifies that a class 3 PD must consume no more than 12.95 W. The reason that the 802.3af standard requires 15.4 W to be reserved to power a 12.95 W device is that the standard requires the PSE to provide enough power for worst-case power loss between the PSE and the PD. Requiring worst-case power reservation at the PSE for every device connected to the PSE limits the number of devices that can be powered by the PSE.
Accordingly, there exists a need for methods, system, and computer program products for efficiently managing the power allocated to a device powered over a communications cable.